Beijing’s municipal government began releasing new air-pollution data over the weekend that will likely raise questions among government critics who worry that authorities aren’t going far enough to better track air quality.

On Saturday, Beijing’s municipal government began publishing hourly measures of what are known as PM2.5 pollutants, or pollutants that measure less than 2.5 micrometers in diameter. But already the data (in Chinese) are showing discrepancies with another measure released hourly by the U.S. embassy in Beijing, long the favored source for air-pollution data for those able to circumvent the Chinese’s government’s Internet censorship efforts.

On Monday morning around 10 a.m., Beijing said PM2.5. levels were measured at about 30 micrograms per cubic meter, which the U.S. Environmental Protection Agency classifies as a “moderate” level of pollution. At roughly the same time Monday morning, the U.S. embassy measured PM2.5 levels of 66 micrograms per cubic meter, which is considered “unhealthy” by U.S. measurements.

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Several reasons could help explain the discrepancy. U.S. and Chinese pollution monitoring locations are located across the city from one another. The U.S. measures PM2.5 levels from equipment at the embassy in eastern Beijing, near the heavily trafficked Third Ring Road. Meanwhile, Beijing’s government releases measurements from a monitoring site in the western Xicheng district, according to state media.

At least one environmental analyst has already begun raising questions about the data, in particular readings from Saturday that measured PM2.5 levels at an extremely low level of three micrograms per cubic meter.

“In all of 2010 and 2011, the U.S. embassy reported values at or below that level only 18 times out of over 15,000 hourly values,” said Steven Andrews, an environmental consultant who studies Beijing’s pollution data, according to the Associated Press. “PM2.5 concentrations vary by area so a direct comparison between sites isn’t possible, but the numbers being reported during some hours seem surprisingly low.”

Beijing has long worried about discrepancies between its data and U.S. pollution data raising suspicion among the Chinese public, and cables released by WikiLeaks have revealed at least one testy conversations between the embassy and Chinese officials, who lamented the U.S. data could confuse Chinese citizens.

State-run media have celebrated Beijing’s new data release as a sign of government openness and responsiveness to citizen demands. Nonetheless, the reliability of the Chinese data remains a question. Local and national officials have historically been accused of manipulating data on everything from food stockpiles to the country’s economic health.

The Chinese government had previously published PM10 pollution levels — that is, pollutants measuring between 2.5 and 10 micrometers in diameters. However, they didn’t previously release data for smaller PM2.5 pollutants, which are smaller and seen by some experts as more harmful to human health.

China hasn’t yet released targets for average annual PM2.5 levels, though the state-run Xinhua news agency in an article on Saturday said the the national standard could be set at 35 micrograms per cubic meter on average per year, citing hearings at the environment ministry from earlier this month.

Strong winds during the weekend blew off much of last week’s especially thick smog in Beijing, leaving behind a relatively rare stretch of consecutive blue sky days to welcome the new PM2.5 readings. It remains to be seen how the Chinese and U.S. data will compare when pollution levels pick up again — something that seems likely to happen before too long.

Both the U.S. Embassy and the Beijing monitoring station showed a massive spike in PM2.5 levels around midnight on Sunday. While it’s not entirely clear what caused the spike, Chinese Internet users speculated it could have something to do with city-wide launching of fireworks to ring in the Lunar New Year.

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